The present invention relates to aircraft flight monitoring devices for improved safety and terrain awareness and more particularly to an integrated terrain awareness system and radio altimeter for use in general aviation aircraft operated under Part 91 of the FAA rules and regulations.
Ground Proximity Warning Devices (GPWS) such as that disclosed in U.S. Pat. No. 3,946,358 are known in the art. The GPWS can prevent aircraft accidents by alerting the pilot to unsafe flight conditions such as proximity to terrain and illogical combinations of airspeed, altitude and aircraft configuration. Unfortunately, these devices are designed for larger aircraft and are generally unsuitable for use in smaller general aviation airplanes. For example, the discrete analog circuitry of some GPWS devices and their associated power requirements are incompatible with the power supplies and space/weight limitations of smaller aircraft. In addition, GPWS devices processes input received from an air data computer and radio altimeter found as separate discrete devices aboard the aircraft. These discrete devices are unlikely to be found on smaller general aviation aircraft due to the additional space and weight required to house them. Furthermore, the complicated design and manufacture of these sophisticated devices makes their cost prohibitive to owners of smaller, general aviation airplanes. As a result, only 20,000 aircraft are equipped with a GPWS system, while an estimated 180,000 aircraft fly without the benefits of this safety enhancing device.
Larger aircraft are also equipped with an additional discrete piece of hardware known as a flight data recorder that further enhances the safety of flight operations. The flight data recorder, or "black box", records various parameters including the aircraft configuration, altitude and airspeed received from multiple sensors located throughout the aircraft. The flight data recorder writes this information to an endless loop magnetic tape, optical disc, other magnetic media, or as an EEPROM. Only a limited portion of the flight, typically one half hour to one hour, is recorded by the flight data recorder. The recorded data is useful for determining the cause of accidents or for monitoring the performance of an individual aircraft and its component parts. The recorded data thus aids in accident prevention by identifying possible changes in flight operations, aircraft component design and maintenance that improve flight safety.
Many light aircraft are also used as training aircraft for student pilots. During the "solo" phase of instruction, the student is permitted to fly without an instructor on board. Without a flight data recorder, however, the instructor has only the student's self appraisal as a basis for evaluating the conduct of such training flights. Furthermore, the limited time record of existing flight data recorders would, even if available, make the record of limited value to the student and instructor.
The flight data recorder and its complicated array of sensors, however, is also too bulky and expensive to be suitable for use on smaller aircraft. In addition to the survivability requirements placed on the flight data recorder housing, the size of the tape drive or disc and associated circuitry also adds to the cubic volume of the recorder. The power requirements of this circuitry is also incompatible with the power available on a smaller aircraft. Thus, smaller aircraft are denied the benefits provided by use of a flight data recorder. Aircraft accident investigations in planes not equipped with flight data recorders must rely on eyewitness accounts and forensic engineering of the aircraft wreckage to determine cause and identify possible life-saving improvements.
Mere miniaturization or substitution of less expensive component parts will not make these safety enhancing devices available to the operator of smaller aircraft. For example, the radar altimeter is a complicated and expensive device that determines the aircraft height above the ground. The majority of aircraft do not have a radio altimeter and are instead equipped with a barometric altimeter that computes height above sea level. Without a radio altimeter, pilots must constantly remain aware of the terrain lying along the flight path to ensure they will not impact the terrain. Many accidents have occurred in which the pilot maintained barometric altitude but, was unaware that the terrain was rising along the flight path. Radio altimeters help eliminate such accidents by providing the pilot with information on position relative to the terrain and are thus a key input into terrain warning devices and accident reconstruction.
Radar altimeters incorporating radar altimeter microwave circuits are typically formed on Teflon circuit boards for optimum microwave performance. Teflon circuit boards, however, are relatively expensive and easily damaged. Substitution of a less expensive glass epoxy material introduces dielectric variations in the board that adversely affect the microwave circuit. In addition, solid state radio altimeters include a microwave transistor and high frequency diodes that must be individually tuned and aligned by hand via tuning stubs located on the circuit board. This process is costly, labor intensive and once completed, the board is optimized solely for the exact microwave circuit and diodes originally installed. Should these components fail, the entire circuit must be replaced and/or retuned. Development of a safety alerting system for light aircraft must therefore include reengineering of the major systems and component subsystems that provide the necessary inputs to the alerting device.